1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an array substrate and a transflective liquid crystal display device including the same.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices have been regarded as next generation display devices providing high added value because of their low power consumption and high portability.
An LCD device is driven based on the optical anisotropy and polarization characteristics of a liquid crystal material. In general, an LCD device includes two substrates, which are spaced apart and facing each other, and a liquid crystal layer interposed between the two substrates. Each of the substrates includes an electrode. The electrodes from respective substrates face one the other. An electric field is induced between the electrodes by applying a voltage is applied to each electrode. An alignment direction of the liquid crystal molecules changes in accordance with a variation in the intensity or the direction of the electric field. The LCD device displays a picture by varying light transmittance according to the arrangement of the liquid crystal molecules.
Active matrix liquid crystal display (AMLCD) devices, which includes thin film transistors as switching devices for a plurality of pixels, have been widely used due to their high resolution and ability to display fast moving images. A related art LCD device will be described hereafter in detail with reference to FIGS. 1–3B.
FIG. 1 is a schematic view of a LCD device according to related art. In the LCD device, first and second substrates 10 and 30 are spaced apart from and facing each other. A liquid crystal layer 50 is interposed between the first substrate 10 and the second substrate 30. At least one gate line 12 and at least one data line 14 are formed on an inner surface of the first substrate 10, which is the side facing the upper substrate 30. The gate line 12 and the date line 14 cross each other to define a pixel region P. A thin film transistor T is formed as a switching element at the crossing of the gate line 12 and the data line 14. Although not shown in detail in FIG. 1, the thin film transistor T includes a gate electrode, a source electrode, a drain electrode, and an active layer. A plurality of such thin film transistors T is arranged in a matrix structure to correspond to other crossings of gate and data lines. A pixel electrode 16, which is connected to the thin film transistor T, is formed in the pixel region P.
The second substrate 30 includes a color filter layer 32 and a common electrode 34 formed on an inner surface of the upper substrate 30, which is the side facing the first substrate 10. First and second polarizers 52 and 54 are arranged over outer surfaces of the first and second substrates 10 and 30, respectively. Each of the first and second polarizers 52 and 54 may be a linear polarizer that transmits only linearly polarized light parallel to the light transmission axis of the polarizer. In addition, a backlight is disposed over the outer surface of the first polarizer 52 as a light source.
The LCD using the backlight as the light source is usually referred to as a transmissive LCD device. In the transmissive type, light incident from the backlight penetrates the liquid crystal panel, and the amount of the transmitted light is controlled according to the alignment of liquid crystal molecules. The amount of the transmitted light is very small for the amount of light incident from the backlight. Only 7% of the light incident from the backlight is transmitted through the liquid crystal panel. Accordingly, the brightness of the backlight should be increased to increase the brightness of the LCD device. Consequently, the transmissive LCD device has high power consumption due to the backlight. To provide enough power to the backlight, a battery is widely used. The battery is heavy, and provides limited operation time.
Transflective LCD devices, which can be used in both a transmissive mode and a reflective mode, have been recently introduced. Since a transflective LCD device uses light emitted from a backlight unit as well as natural or artificial ambient light, the transflective LCD device can be used under various lighting conditions, and has decreased power consumption. A transflective LCD device of the related art will be described hereinafter more in detail.
FIG. 2A is a plan view of an array substrate for the transflective LCD device according to related art. In FIG. 2A, a gate line 62 and a data line 70 cross each other, and a thin film transistor T is formed at a crossing of the gate line 62 and the data line 70. A crossing region of the gate line 62 and the data line 70 define a pixel region P. A pixel electrode 88 connected to the thin film transistor T is formed in each pixel region P. Although not shown in detail in the figure, the pixel electrode 88 includes a reflector, which has an opening 80 in the middle of the pixel region P, and a transparent electrode, which covers the reflector. The pixel electrode 88 overlaps the gate line 62 and the data line 70, and the transflective LCD device has a high aperture ratio.
Disclination occurs along edges of the pixel electrode 88 due to abnormal arrangement of liquid crystal molecules. Disinclination causes light leakage. In an LCD device including the above array substrate, since the pixel electrode 88 overlaps the gate and data lines 62 and 70 that are opaque, the gate and data lines 62 and 70 block light leakage around the edges of the pixel electrode 88. Additionally, the aperture ratio increases in accordance with the area of the pixel electrode 88. Thus, a reduction in contrast ratio due to light leakage is prevented in a high aperture ratio LCD device.
The overlap of the gate and data lines 62 and 70 by of the pixel electrode 88 causes a parasitic capacitance. The parasitic capacitance causes crosstalk. To minimize problems associated with crosstalk, an organic insulating material having relatively low dielectric constant is generally disposed between the gate and data lines 62 and 70 and the pixel electrode 88.
A portion of the pixel region P is referred to as a transmissive area TA. The transmissive area TA corresponds to the opening 80. The backlight is used as a light source within the transmissive area TA. The other portion surrounding the transmissive area TA is referred to as a reflective area RA. Ambient light is used as the light source within the reflective area RA.
FIG. 2B is a cross-sectional view of the related art transflective LCD device taken along the line IIB—IIB depicted in FIG. 2A The overlap of the pixel electrode and the gate and data lines will be explained in detail with reference to FIG. 2B. In FIG. 2B, a gate insulating layer 66 is formed on a substrate 60 and the data line 70 is formed the gate insulating layer 66. A first passivation layer 76 and a second passivation layer 78 sequentially formed covers the data line 70. Reflectors 82 are formed on the second passivation layer 78 such that adjacent reflectors 82 overlap respective sides of the data line 70. An inter insulating layer 84 is formed on the reflector 82. Transparent electrodes 86 are formed on the inter insulating layer 84. The transparent electrodes 86 correspond to the reflectors 82. One reflector 82 and a corresponding transparent electrode 86 constitute the pixel electrode 88.
In FIG. 2B, each of a first reflector 82 and a first transparent electrode 86 overlaps a first portion of the data line 70. The first reflector 82 and the first transparent electrode 86 are located on the left side of the data line 70, in the context of FIG. 2B. A second portion of the data line 70 is also overlapped by each of a second reflector 82 and a second transparent electrode 86. The second reflector 82 and the second transparent electrode 86 are located on right side of the data line 70, in the context of FIG. 2B. The second reflector 82 and the second transparent electrode 86 are adjacent to the first reflector 82 and the first transparent electrode 86, respectively. The first overlapped portion of the data line has a width d1. The second overlapped portion of the data line has a width d2. A distance between adjacent reflectors 82 or between adjacent transparent electrodes 86 is designated by d3.
As shown in FIG. 2A, when a rubbing direction r1 is defined as a diagonal direction from a lower-right side to an upper-left side, there are no rubbing problems because a rubbing fabric (not shown) travels from top to bottom in a right-stepping area A1 of the data line 70. However, in a left-stepping area A2 of the data line 70, since the rubbing fabric travels from bottom to top, rubbing may cause light leakage. To prevent light leakage, the width of the portion of the data line overlapped by the pixel electrode should be increased.
FIG. 3A illustrates an increase in the width of a transparent electrode in another array substrate for a transflective LCD device according to the related art. In FIG. 3A, a width of a transparent electrode 90 of the left side of data line 92 in the context of the figure is increased. Accordingly, the width of the left portion of the data line 92 that is overlapped by the left transparent electrode 90 also increases. Therefore, an overlap width d11 of the left portion of data line 90, which is overlapped by the left transparent electrode 90, is larger than an overlap width d12 of the right portion of data line 90, which is overlapped by of the right transparent electrode 94.
A distance d13 between the left and right adjacent transparent electrodes 90 and 94 decreases in accordance with the increase in the overlap width d11, in comparison with the array substrate depicted in FIG. 2B. If the distance d13 is very narrow, that is, if the distance between patterns, such as reflectors or transparent electrodes, is very narrow, forming the patterns by a photolithographic process is problematic due to the limited resolution of an exposing apparatus.
FIG. 3B illustrates an increase in a width of a data line in another array substrate for a transflective LCD device according to related art. In FIG. 3B, the data line 96 is extended to the left. Accordingly, the width of the left portion of the data line 96 that is overlapped by the left transparent electrode 98 also increases. However, the pixel area is deacreased by the above method, thus reducing the aperture ratio.
Therefore, in the related art transflective LCD device with a high aperture ratio, it is difficult to sufficiently increase the width of an overlapped portion of the gate and data lines by the pixel electrode due to processing limitation from an exposing apparatus. In addition, the aperture ratio decreases when the width of the overlapped portion increases.